This invention relates to a shutter plate control device in a disc playback device of a type in which a disc magazine case housing a disc is loaded in a main body and, more particularly, to a device capable of controlling a shutter plate provided for opening and closing a slot formed in the disc magazine case for exposing the disc to a pickup head.
In a disc playback device of a type in which a disc magazine case housing a disc is loaded in a main body of the device for playback of the disc, a slot is formed in the disc magazine case for exposing the disc housed in the disc magazine case to the outside and this slot faces a pickup head so as to enable data recorded on the disc to be read by the pickup head.
There is a prior art disc playback device using a disc magazine case including a shutter plate which opens and closes the slot for reading data. In taking out this disc magazine case from the main body of the device, this slot is closed by the shutter plate for preventing dust from entering the inside of the disc whereas during playback of the disc, the slot is opened to enable data on the disc to be read by the pickup head.
FIG. 17 shows the prior art disc playback device using the above described disc magazine case which is disclosed in the U.S. patent application No. 751,731 filed on July 3, 1985.
FIG. 17, reference character 1 designates a disc magazine case, 2 a disc housed in the disc magazine case and 3 a main body of the device. The disc magazine case 1 is formed in its bottom plate 4 with a laser beam slot 5 for reading data recorded on the disc, and on one side thereof with a rack 6 and is provided with a shutter plate 7 inside of the case. The shutter plate 7 is rotatable in the directions of arrows P1 and P2 about a pin 9 of a shutter lever 8 fixed to the shutter plate 7. In the illustrated state, the shutter plate 7 is closing the slot 5. When it is rotated in the direction of the arrow Pl to a position in which a slot 10 of the shutter plate 7 is in register with the slot 5, the slot 5 is opened. The shutter plate 7 normally closes the slot 5 by being urged in the direction of arrow P3 by a spring 11. The main body 3 comprises a loading device including a loading pinion 12 which can mesh with the rack 6 and an engaging portion 13 which is engageable with the tip portion of the shutter lever 8.
Operation of this device will be briefly described. When the disc magazine case 1 is inserted into the main body 3, the loading pinion 12 meshes with the rack 6 and thereafter the loading pinion 12 is rotated by the loading device causing the disc magazine case 1 to be moved in the direction of the arrow P3, i.e. towards the main body. In a later stage of this movement of the disc magazine case 1, the tip portion of the shutter lever 8 engages the engaging portion 13. By the loading operation, the shutter lever 8 is further pushed in the direction of the arrow P3 so that the shutter plate 7 is rotated in the direction of the arrow P1 against the force of the spring 11 thereby opening the slot 5. Upon being moved to a predetermined position, the disc magazine case 1 abuts against a stop 14 and ceases its movement in the direction of the arrow P3. The loading device, however, continues to supply a pulling force overcoming the force of the spring 11 to the rack 6 through the loading pinion 12 owing to operation of a slip clutch (not shown) provided in the loading device. In this state, the disc magazine case 1 is lowered and the disc 2 in the disc magazine case 1 is placed on a turntable (not shown).
Since this disc playback device is so constructed that the shutter plate 7 is rotated in the direction of the arrow P1 against the force of the spring 11 during loading of the disc magazine case 1, the shutter plate 7 can always be closed automatically by the force of the spring 11 except while the slot 5 needs to be opened. On the other hand, the urging force of the spring 11 constitutes a load to a drive source of the loading device during the loading operation with a result that the drive source must be of a large power. Further, this device requires the slip clutch in the loading device for maintaining the disc magazine case 1 to be pulled in the direction of the arrow P3 against the force of the spring 11 during the lowering of the disc magazine case 1 with a result that the construction of the main body 3 of the device becomes complicated. If the spring 11 is omitted from the disc magazine case 1, the slip clutch in the loading device in the main body will be obviated but in this case the structure for opening and closing the shutter plate 7 must be all provided on the side of the main body 3 and a complicated construction caused thereby is undesirable. Further, if the spring 11 is omitted, whether the shutter plate 7 is in the open state or closed state is quite uncertain when the disc magazine case 1 is inserted into the main body. The device will therefore require construction which will ensure a smooth loading operation regardless of the state of the shutter plate 7 and an accurate opening and closing operation of the shutter plate 7.
It is, therefore, an object of the invention to provide a shutter plate control device in a disc playback device capable of reducing load applied to the drive source of the loading device.
It is another object of the invention to provide a shutter plate control device with a simplified construction of the main body of the disc playback device.
It is still another object of the invention to provide a shutter plate control device capable of accurately controlling the operation of the shutter plate during the loading operation regardless of the state of the shutter plate.